Positionable carriage assemblies for supporting and positioning a load are known. Some positionable carriage assemblies include a rack and pinion drive system wherein one or more driven carriage arms include a rack driven by a hydraulic or electric motor having a pinion gear. Where precise positioning of such systems is desired, these types of carriage assemblies can have limitations. For example, due to the construction of hydraulic motors, the exact position of the pinion gear cannot be reliably ascertained with a high degree of accuracy. Variations in hydraulic fluid temperature can also affect accuracy. These types of limitations can result in hunting of the control system. Carriage assemblies of this type can also require a high number of parts, resulting in increased costs and decreased reliability. In addition, some implementations can also result in excessive wear on the motor(s), and in particular the bearings. Furthermore, many existing systems require significant space for the mounting of the motor(s) and other related components. Accordingly, a need exists for a durable and compact positionable carriage assembly with few moving parts that can be accurately and reliably positioned.
One non-limiting application of a positionable carriage assembly is in a directional drilling machine application. Directional drilling machines are used to drill holes along a generally horizontal path beneath the ground. After a hole is drilled, a length of product (e.g., cable, pipe or the like) can be passed through the hole. Such directional drilling machines eliminate the need for digging a long trench to lay a length of product underground.
A typical directional drilling machine includes an elongated track that can be aligned at an inclined orientation relative to the ground. A drive head is mounted on the track so as to be moveable along the length of the track. The drive head includes a drive member that is rotated about a drive axis that is generally parallel to the track. The drive member is adapted for connection to a length of pipe. For example, the drive member can include a threaded end having either female or male threads.
To enhance drilling productivity, it is important to maximize the efficiency in which pipes can be loaded into and unloaded from the magazine of a directional drilling machine. Until fairly recently, pipes were manually carried between the magazine and the drive head of a drilling machine, and were also manually loaded into and unloaded from the magazine. Recent developments have improved pipe loading and unloading efficiencies through automation. For example, U.S. Pat. No. 5,556,253 to Rozendaal et al. (the '253 patent), and U.S. Pat. No. 5,607,280 (the '280 patent) to Rozendaal, disclose improved pipe loading/unloading devices. The '253 and '280 patents disclose devices that effectively use gravity to automatically unload pipes from a magazine. The '253 and '280 patents also disclose devices each having pipe transfer members that automatically move pipes between a magazine and a drive head. The advances provided by the devices disclosed in the '253 and '280 patents have assisted in significantly improving a drill operator's ability to enhance drilling productivity. PCT Publication WO 2012/075289 (the '289 publication) to Novelo also discloses a system including shuttles for moving pipes between a drill rod magazine and the drive head. Each of U.S. Pat. No. 5,556,253; 5,607,280; and PCT WO 2012/075289 is hereby incorporated by reference in its entirety.